Welcome to the DIS!!!!! I know it can be very overwhelming with so much info out there. We have been on the Eastern 7-day twice and are going on the Western in August so I do not have too much personal experience info to give you.
On
Castaway Cay you can rent banana boat rides, parasailing,. The snokerling is better on the o ther island than on CC. The water there gets stirred up from everybody and can make it difficult to see very far. We ususally just hang out and relax on CC.
To get back and forth to the ship you just walk. The ship docks pretty close to the shopping area at each port. CC has about a 10 minute walk to the beach area for you can take a tram (walking is quicker because the tram fills up so quickly).
You are correct that not much is included once you are off the ship. The exception is Castaway Cay where a BBQ lunch is provided. There is also bar service which is extra, but they have a wonderful fresh fruit buffet and ice water, fruit punch and either lemonade or ice tea complimentary.
Make sure you tell the 17 & 14 year olds to attend the teen 411 meeting the first night of the cruise at Common Grounds. There will be an invitation in the stateroom for them the first day. This is where all the teens meet and get to know each other. Most break into groups and hang out the whole cruise together. I have a son 17, a daughter 18 and a daughter 14. WE have sailed 5 times on
DCL and they are still keeping in touch with teens from all the previous cruises!!!!
Hope I helped answer a few questions. Just keep reading these boards and you will be amazed at the info you can learn.
Have fun!!!! and don't hesitate to ask .....no question is dumb!!! We are sailing a few weeks after you on 8/3!!
Where in Northern NJ are you. I used to work in Ramsey/Mahwah and my dad has owned a business in Ho-Ho-Kus for over 40 years.
MJ